The RCS Media Specialists' Recommendations:

Emergent Readers (Additional Emergent Titles)
Early Readers (Additional Early Titles)
Transitional Readers (Additional Transitional  Titles)
Expanding Readers (Additional Expanding Titles)
Refining Readers (Additional Refining Titles)
Proficient Readers (Additional Proficient Titles)
Beyond Proficient Readers (Additional Beyond Proficient Titles)

Leveled Books A-Z (Fountas and Pinnell)
Levels A-G     Levels H-N    Levels O-T    Levels U-Z    Full List

Scholastic Book Wizard (Tutorial)